a)
\(\dfrac{2x}{3x+3}=\dfrac{2x}{3\left(x+1\right)}=\dfrac{2x\left(x+2\right)}{3\left(x+1\right)\left(x+2\right)}\)
\(\dfrac{2x-1}{\left(x+1\right)\left(x+2\right)}=\dfrac{6x-3}{3\left(x+1\right)\left(x+2\right)}\)
b)
\(\dfrac{2-x}{x-1}=\dfrac{\left(2-x\right)\left(x-1\right)\left(x+1\right)}{\left(x-1\right)^2\left(x+1\right)}\)
\(\dfrac{3x+1}{x^2-1}=\dfrac{3x+1}{\left(x-1\right)\left(x+1\right)}=\dfrac{\left(3x+1\right)\left(x-1\right)}{\left(x-1\right)^2\left(x+1\right)}\)
\(\dfrac{1}{\left(x-1\right)^2}=\dfrac{x+1}{\left(x-1\right)^2\left(x+1\right)}\)